Fall Armyworm Moth

Appearance

The adult moths are 32 to 40 millimetres wing tip to wing tip, with a brown or gray forewing, and a white hindwing. There is slight sexual dimorphism, with males having more patterns and a distinct white spot on each of their forewings. The first larval instar is light colored with a larger dark head. As they develop through instars, they become browner with white lengthwise lines. They also develop dark spots with spines.

Naming

The fall armyworm may be presently undergoing a divergence into two separate species. These two strains have major genetic differences that are connected to the plants they feed on, even though both still exist in the same area . These two strains can be loosely categorized into a rice strain and a corn strain. This separation is occurring because of differences in habitat , and differences in reproductive behavior. The reproductive differences can be divided into two categories: difference in the timing of mating at night, and difference in female sex pheromones.

Status

It is regarded as a pest and can damage and destroy a wide variety of crops, which causes large economic damage. Its scientific name derives from ''frugiperda,'' which is Latin for ''lost fruit'', named because of the species' ability to destroy crops. Because of its propensity for destruction, the fall armyworm's habits and possibilities for crop protection have been studied in depth. It is also a notable case for studying sympatric speciation, as it appears to be diverging into two species currently. Another remarkable trait of the larva is that they practice cannibalism as a disease control mechanism.

The fall armyworm is active at a different time of year from the true armyworm, another species in the order Lepidoptera and family Noctuidae, but of the genus Mythimna. Outbreaks of the true armyworm usually occur during the early part of the summer; the fall armyworm does most damage in the late summer in the southern part of the United States, and early fall in the northern regions.

Behavior

A female attracts males by perching atop the host plant feeding area and releasing a sex pheromone as the signal that she wishes to mate. The pheromone has been studied and found to contain the components Z7-12 and Z9-14. Each female only mates once per night; this creates a physical conflict between the multiple males that will fly towards a ready female. There is an order to which the females call and mate: virgin females do first, females who have mated once next, and females who have already mated multiple times call and mate last during the night.

Reproduction

The larvae go through six different instars, each varying slightly in physical appearance and pattern. The larva process lasts from 14 to 30 days, again depending on temperatures. The mature caterpillar is about 1+1⁄2–2 inches in length. This is the most destructive life stage as the larvae have biting mouth parts. The larvae have a distinctive inverted Y suture on the forehead.

Predators

Fall armyworm caterpillars are directly preyed upon by many invertebrates and vertebrates. Common predators include birds, rodents, beetles, earwigs, and other insects. It has been shown that direct predation can cause significant losses to caterpillar populations. The larva's main defense against enemies is their ability to reach large numbers and migrate before seasonal conditions are suitable for predators.

Migration

Adults are capable of flying long distances, so even though they are unable to overwinter north of the southern region of the United States, the moths can migrate as far north as southern Canada in warm months. Their migration rate is remarkably fast, estimated at 300 miles per generation. Some scientists speculate that this fast migration is aided by the movement of air in weather fronts.

Evolution

The fall armyworm's life cycle is completed within 30 days during summer, and 60 days during the spring and autumn seasons; during the winter, these caterpillars' life cycle lasts about 80 to 90 days.[3] The number of generations a moth will have in a year varies based on climate, but in her life span a female will typically lay about 1,500 eggs. Because larvae cannot enter into diapause they cannot survive cold temperatures.